The field of the invention is printing apparatus and more particularly the invention is concerned with the construction of cylinders for transferring pigment to a substrate using electrostatic techniques. The advantages of the invention are especially applicable in the printing of multicolor images on substrates which are either in long strip form or in the form of sheets of paper, fabric and the like.
Multicolor printing by conventional presses is a complex process from the point of making the color separations, forming the cylinders, operating the presses, providing the pigment or inks for the separate cylinders or other plates, etc.
Several developments in recent years have pointed to the use of electrostatic techniques for multicolor printing in printing presses using electrostatic techniques. As known, photoelectrostatic imaging is effected by charging the surface of a photoconductive coating in darkness, exposing the same to a light image, then toning the latent image with fine particles either in powder form or suspended in a solvent. The toned or developed image may either be transferred to a receptor or it may be fused in place directly onto the electrophotographic member of which the photoconductive coating is a part.
One of the coatings which has been evolved recently is a high gain, high resolution, easily charged, fully dischargeable, wholly inorganic, microcrystalline photoconductive material which has especially the property that it is rugged and extremely flexible when coated onto a thin flexible substrate. The material is disclosed in U.S. Pat. No. 4,025,339. This coating is advantageous in addition to being flexible in that it can be imaged quickly in a high speed press and discharged readily by ambient light so that, as will be explained, it may be provided with an image of toner that is insulating and thereafter charged to apply a charge to the insulating toner while permitting the charge on the untoned areas to be dissipated in light. Then secondary toner can be adhered to the primary toned image and transferred to a substrate.
Thin-walled metal sleeves of electrodeposited nickel, copper or other metal have been used in the fabric and other substrate printing field with success. These sleeves are a fraction of a millimeter thick and can be several meters long and as much as a third of a meter in diameter. They are seamless and are readily supported in printing machines. The sleeves which have been used heretofore are disclosed in U.S. Pat. No. 2,287,122 and have been foraminous in order to enable ink or other pigment to be expressed by doctor means through the walls of the cylinders onto the passing substrate. The walls are provided with suitable designs in the surface blocking certain of the holes and leaving others open.
For electrostatic use, these sleeves are sputtered with coatings of the photoconductive material which has been mentioned and are imperforate. An important advantage of this type of sleeve is that it is light in weight, it is quite strong and is collapsible so that packing and shipping the same is economical. In using the sleeves they must be mounted in cylindrical form on the printing press to receive and transfer the pigment. They need to be supported on their interiors by using some readily installed or removed device which must maintain the sleeves in rigid cylindrical form all the period of time that the cylinders are in use.
The invention contemplates the provision of the means for enabling the sleeves with photoconductive coatings to be used efficiently and easily.
Reference may be made to the following prior art: Rothwell U.K. Pat. No. 789,177, published Jan. 15, 1958; Klemm W. German Auslegeschrift No. 1,231,258 published Dec. 29, 1966 Zimmer Austria Pat. No. 240,879, June 25, 1965; Zimmer W. German Auslegeschrift No. 1,181,237 published Nov. 12, 1964 Wagter U.S. Pat. No. 3,372,801, Mar. 12, 1968.
All of these references but the last disclose the pressurizing of sleeves by means of an inflatable tube. The instant invention, in one of its forms uses an inflatable elastomeric tube for inflation, but it is important to recognize that in the prior art the cylinders are being processed to have a pattern applied on their exterior (U.K. No. 789,177; DAS No. 1,181,237; Austria No. 240,879) or to produce a sleeve in a galvanic process (DAS No. 1,181,237). The use of a pressurized sleeve for a printing process and its mounting in a high speed printing press is not disclosed, taught or contemplated by this prior art. The U.S. patent referred to merely relates to the packing of flexible sleeves as explained herein.